1. Field of the Description
The present description relates, in general, to methods of fabricating lightweight, high-strength plastic or elastomeric products, and, more particularly, to a method for utilizing a rotocast composite hybrid process to mold a composite or multi-layer product or part, such as a three-dimensional hollow part, that has improved strength and stiffness and is lighter weight than typical molded pieces produced using rotocasting processes and less expensive than a typical composite part.
2. Relevant Background
There are many applications for lightweight, higher strength products that are formed of a plastic such as an elastomer (e.g., urethane or the like). In one specific example, costumes worn by actors in theatrical and theme park settings are often formed using molding techniques. The costumes may be worn for long periods of time in higher temperature settings such as under bright lights or under the Sun in the summer. To avoid actor fatigue, it is desirable to make the costume components as lightweight (e.g., thin) as practical while still providing a relatively strong and durable costume that can be worn many times. However, the processes/techniques described herein may be used to form any three-dimensional hollow shape where the performance of a composite is desired but at a lower cost.
Composite materials, such as reinforced plastics made of a combination of materials including a binder or reinforcing constituent blended into the base material prior to molding, can be used in some cases for molding costume elements and other parts. Composites are useful as they can be used to mold strong, stiff, and lightweight products. Unfortunately, cost is often a limiting factor for many products, and composites are often relatively expensive, making them prohibitively expensive for many applications. Another problem with the use of composites may be mold parting lines and a need for body work and painting to achieve a desired appearance. For example, a three-dimensional element may be molded out of composite in multiple sections that are tied together in a secondary step that results in parting lines. The gel coating requires painting, which can be expensive, and the parting lines need an extensive amount of body work prior to painting so as to produce an acceptable quality surface. These additional steps further drive up the cost of the composite part. Also, a painted part will require periodic painting or maintenance to retain an acceptable appearance. Some of the resins used with this process may enable the finished color to be pigmented into the skin, eliminating the need for painting.
Parts or products may also be formed using more economical processes such as rotocasting (or rotomolding). In a typical rotocasting process, a two-part mold (or mold formed by two mating halves) of a product is produced that has a small fill hole or sealable inlet. A two-part resin, such as epoxy, polyurethane, or polyester, is mixed and then injected through the fill hole into the interior chamber or volume of the mold. The mold is supported within a rotocaster or rotocasting machine, and the rotocasting machine is operated to rotate the filled mold along both the X and Y axes to produce a coating of uniform thickness on the inner surfaces of the mold. After curing, the mold is opened and the molded part is removed for use or for further processing such as sanding to remove part lines and painting to provide a desired outer appearance or color. While rotocasting of parts is economical, the resulting parts are often not very strong or, if thick enough to be strong, are not very lightweight. An un-reinforced plastic will also not have the stiffness of a composite, which provides better shape retention of a three-dimensional object, particularly when used in a warm environment.
Hence, there remains a need for an improved method of forming lightweight and strong/durable three-dimensional parts or elements that also controls material, manufacturing/finishing, and maintenance costs. Preferably, such a method would provide parts or products with relatively thin walls and would be adaptable to limit the need for painting and/or other post-curing processing.